1. Field of the Invention
This invention relates generally to power transmissions having fluid actuated ratio establishing devices and, more particularly, to a control arrangement for improving the performance of a fluid actuated rotating clutch.
2. Description of the Prior Art
Power transmissions of the planetary gear type typically include a plurality of planetary gear sets and fluid pressure actuated clutches for selectively interconnecting elements of one gear set with elements of another. Some of these clutches rotate during and after application so that fluid introduced into the rotating clutch at an apply pressure precisely regulated to control shift quality develops an additional centrifugal component varying with speed of clutch rotation. The centrifugal pressure component acts in addition to or with the apply pressure and, due to its variable nature, renders control of shift quality more difficult. To overcome this difficulty, rotating clutches have been proposed wherein a secondary or balance chamber is formed on the side of the clutch piston opposite the primary or apply pressure chamber so that when both chambers are filled with fluid and the clutch is rotating, substantially equal and oppositely directed centrifugal pressure components are developed which balance each other and render clutch application dependent solely on the fluid apply pressure as precisely regulated by the transmission control. In such designs, however, the centrifugal pressure components are always balanced so that increasing the ultimate torque capacity of the clutch requires an increase in ultimate or maximum apply pressure. In a rotating clutch having a control according to this invention centrifugal pressure components are balanced during clutch application for optimum shift quality control and unbalanced at full clutch application to improve the torque capacity of the clutch without resort to higher ultimate clutch apply pressure.